active visual perception and cognition
My research focuses on dynamic processes of visual perception and cognition in active observers. In my group at Humboldt University (www.rolfslab.de), we combine eye tracking, motion capture, psychophysics, and computational modelling to understand the impact of movements of the body — from small-scale microsaccades, over reach movements, to large-scale eye-head gaze shifts — on visual and cognitive functions. In collaborations, I am actively expanding my fields of interest and supplement my core methods with physiological measurements (EEG) and studies in clinical populations whenever these promise additional insights into the questions at hand. Here is a short list of topics that I feel I made a contribution to:
attention in active vision
The main body of my work over the last years has addressed how the movements of our eyes, heads, and bodies confine what we perceive and how we perceive it. It's fairly obvious that re-orienting our retinae's sweet spots towards relevant parts of the visual scene determines what we will see in detail (at the fovea) and what we will remain in peripheral vision. However, we also know that — in the service of our behavioral goals — the brain processes some parts of the visual scene with high priority while ignoring others (covert attention), and it turns out that overt, goal-directed movements and covert shifts of attention interact quite strongly. One goal of my research has been to determine the nature and function of these interactions.
During my postdoc at with Marisa Carrasco at NYU, for instance, we showed that in the last moments before a saccade, a marked increase in visual sensitivity at the saccade goal is accompanied by an enhancement of subjective stimulus intensity (perceived contrast). With Bonnie Lawrence, we examined how this finding generalizes to a different class of goal-directed movements — reaches. My current PhD student, Zampeta Kalogeropoulou, takes a closer look at the role of feature-based attention in active vision.
Rolfs, M., Lawrence, B., & Carrasco, M. (2013). Reach preparation enhances visual performance and appearance. Philosophical Transactions of the Royal Society B: Biological Sciences, 368, 20130057. [pdf]
Rolfs, M. & Carrasco, M. (2012). Rapid simultaneous enhancement of visual sensitivity and perceived contrast during saccade preparation. Journal of Neuroscience, 32, 13744-13752. [pdf]
perceptual continuity in the moving observer
When I started a postdoc in the new lab of Patrick Cavanagh in 2008, we started working on understanding visual direction constancy, or, spatiotopy. That is, why seems visual perception so remarkably continuous in space and time despite the fact that eye-, head-, and body-movements produce large-scale transitions in the input stream on the retina? And how do we keep track of things are around us if they jump incessantly across our receptors? Inspired by neurophysiological findings of predictive remapping in saccade- and attention-related brain areas (LIP, FEF, SC), Donatas Jonikaitis, Heiner Deubel, Patrick, and I were able to show that spatial attention is updated to new retinal locations just before a saccade is executed, compensating for the impending shift of the visual scene on the retina. In a continued collaboration with Patrick, Donatas, and Martin Szinte, we found that this remapping of attention serves perceptual continuity across saccades.
In another project, together with Tomas Knapen, my ever-so enthusaistic office-mate in Paris, we probed the reference frames of a number of visual aftereffects, to look into the transfer of feature information across eye movements. Nothing really transferred — the tilt and the motion aftereffect appeared to be entirely retinotopic. In another productive collaboration with Thérèse Collins (then at the University of Hamburg), we showed that the visual system has very reliable information about how the eyes are moving. I am currently involved in a collaboration with Katy Thakkar that looks into the loss of this information clinical populations.
Rolfs, M., Jonikaitis, D., Deubel, H., & Cavanagh, P. (2011). Predictive remapping of attention across eye movements. Nature Neuroscience, 14, 252-256. [pdf]
Cavanagh, P., Hunt, A. R., Afraz, A., & Rolfs, M. (2010). Visual stability based on remapping of attention pointers. Trends in Cognitive Sciences, 14, 147-153. [pdf]
Knapen, T., Rolfs, M., & Cavanagh, P. (2009). The reference frame of the motion aftereffect is retinotopic. Journal of Vision, 9(5):16, 1-6. [pdf]
Collins, T.*, Rolfs, M.*, Deubel, H., & Cavanagh, P. (2009). Post-saccadic location judgments reveal remapping of saccade targets to non-foveal locations. Journal of Vision, 9(5):29, 1-9. [pdf] (*authors contributed equally)
active visual cognition
Over many years, I have been very interested in visual cognition, that is the seemingly high-level functions (e.g., memory, recognition, inference) that visual processing is capable of. The first visible sign of my interest, however, appeared no earlier than 2013. In this collaboration with Michael Dambacher at the University of Konstanz and Patrick Cavanagh in Paris, we found visual adaptation of the perception of causality. Our results suggest the existence of visual routines in retinotopic cortex that detect and adapt to cause and effect. We showe this using very simple collision stimuli, but I am interested in taking this project further in the foreseeable future.
In a different, rather unrelated project with my postdoc Sven Ohl, we are currently investigating the impact of goal-drected movements on visual memory. Sven finds very strong interactions between action and memory, so this is likely to become a major topic in our lab.
Rolfs, M., Dambacher, M., & Cavanagh, P. (2013). Visual adaptation of the perception of causality. Current Biology, 23, 250-254. [pdf]
fixational eye movements
Human visual perception almost completely relies on the fact that the eyes are able to fixate points within a visual scene. But the term fixation may easily be misunderstood. We never fixate perfectly and we can count ourselfes lucky in this regard, since small eye movements during fixation clearly mediate perception. Fixational eye movements prevent the visual world from fading. My research focusses mainly on microsaccades, small flicks of the eye during intended fixation. For some decades, there was reasonable doubt in the purpose of these small movements. Over the last ten years, however, neurophysiological findings and improved eye-movement-recording techniques pushed the topic over the surface again and doubts diminished in the light of new evidence. If you're interested, take a look at my fairly exhaustive review on that topic in Vision Research.
During my PhD I studied what microsaccades tell us about the workings of the oculomotor system and had a few key insights. In one series of experiments, for instance, we (together with Ralf Engbert, Jochen Laubrock, & Reinhold Klieglat the Universität Potsdam) linked microsaccade rate and direction to spatial attention in vision and audition. In another study, we found that microsaccades may be associated with both a shortening or a lengthening of subsequent saccade latencies, depending on the amplitude of the microsaccade and on when it was observed relative to the saccade. These results have important implications for the generation of microsaccades and saccades and provided the basis for a model of microsaccade and saccade generation. In particular, it made predictions about the site of microsaccade generation in the brain that later found strong and independent neurophysiological support.
Rolfs, M. (2009). Microsaccades: Small steps on a long way. Vision Research, 49, 2415-2441. [pdf]
Rolfs, M., Kliegl, R., & Engbert, R. (2008). Towards a model of microsaccade generation: The case of microsaccadic inhibition. Journal of Vision, 8(11):5, 1-23. [pdf]
Rolfs, M., Laubrock, J., & Kliegl, R. (2006). Shortening and prolongation of saccade latencies following microsaccades. Experimental Brain Research, 169, 369-376. [pdf]
Rolfs, M., Engbert, R., & Kliegl, R. (2004). Microsaccade orientation supports attentional enhancement opposite to a peripheral cue. Psychological Science, 15, 705-707. [pdf]
Some people develop remarkable skill at efficiently distributing spatial attention across the visual field. For instance, linesmen in soccer games almost flawlessly report when players are offside (i.e., at the moment the ball is played by one of his team, a player involved in active play is nearer to his opponents' goal line than both the ball and the second to last opponent). Such complex abilities require learning to attend to parts of the visual scene (e.g., a handful of relevant players distributed across the pitch) while effectively ignoring most other information that is available. Attentional learning has become a recurring theme in my research agenda and I hope it can become a more prominent one in the future. In a project with Alex White, for instance, we found that these presaccadic attention shifts can be shaped by recent experience. In a project with Annette Kinder, we showed that the oculomotor system learns to effectively prepare for movements towards important parts of a scene and inhibit others where relevant information is unlikely.
White, A.L., Rolfs, M., & Carrasco, M. (2013). Adaptive deployment of spatial and feature-based attention before saccades. Vision Research, 85, 26-35. [pdf]
Kinder, A., Rolfs, M., & Kliegl, R. (2008). Sequence learning at optimal stimulus-response mapping: Evidence from a serial reaction time task. Quarterly Journal of Experimental Psychology, 61, 203-209. [pdf]
oculomotor control and plasticity
Finally, what are the basic processes underlying saccade generation and targeting? And how do they adapt to internal or external changes? approached this question was concerned with the gap task, a classical oculomotor paradigm, in which a fixation stimulus disappears prior to the appearance of a new fixation target. We know that the oculomotor system is put in some state of readiness during the gap period. However, it is not entirely clear whether this preparation is purely temporal or whether there is spatially localized preparation (i.e., specific saccade metrics are prepared). Together with Francoise Vitu (CNRS, Marseille), we have developed a new version of the gap paradigm in which we aimed to distinguish between these two scenarios. It turned out that purely temporal preparation cannot account for saccadic behavior in the gap task.
Rolfs, M., Knapen, T., & Cavanagh, P. (2010). Global saccadic adaptation. Vision Research, 50, 1882-1890. [pdf]
Rolfs, M. & Vitu, F. (2007). On the limited role of target onset in the gap task: Support for the motor-preparation hypothesis. Journal of Vision, 7(10):7, 1-20. [pdf]